Controlling vegetation with benzyl thiopyridine oxides



United States Patent 1964. Divided and this application Jan. 20, 1964,Ser.

5 Claims. (Cl. 712.5)

This application is a division of application Serial No. 180,853, filedMarch 19, 1962, now US. Patent 3,155,671, granted November 3, 1964.

This invention relates to a class of benzyl thiopyridine oxides and tothe preparation thereof. More particularly, this invention relates toderivatives of Z-thiopyridine, 1- oxide which destroy or controlundesired vegetation.

The compounds of the present invention may be represented by thefollowing general formula:

in which R represents halobenzyl, the number of halogen atoms being lessthan five. The halogen is preferably chlorine but bromine and to alesser extent fluorine and iodine are also suitable. In general,halogenated benzyl comprise monohalobenzyl, 2,3-, 2,4-, 2,6- or3,6-dihalobenzyl, 2,3,4-, 2,3,6-, 2,4,5- or 2,4,6-trihalobenzyl,2,3,4,5- or 2,3,5,6-tetrahalobenzyl, alpha-methyl 2,6-dihalobenzyl andalpha-methyl 2,3,6-trihalobenzyl. Examples of the new compounds comprise2-(o-methylbenzylthio)pyridine, l-oxide 2-(p-methylbenzylthio)pyridine,l-oxide 2-(o-chlorobenzylthio)pyridine, l-oxide2-(m-chl0robenzylthio)pyridine, l-oxide 2- p-chlorobenzylthio pyridine,l-oxide 2-(2,4-dimethylbenzylthio) pyridine, l-oxide 2-2,6-dimethylbenzylthio pyridine, l-oxide 2-(2,3-dichlorobenzylthio)pyridine, l-oxide 2-(p-fluorobenzylthio pyridine, l-oxideZ-(p-bromobenzylthio) pyridine, l-oxide 2- (m-bromobenzylthio pyridine,l-oxide 2-(2,6-diiodobenzylthio)pyridine, l-oxideZ-(m-fluorobenzylthio)pyridine, l-oxide 2-(3,6-dichlorobenzylthio)pyridine, l-oxide 2- o-fiuorobenzylthio pyridine, l-oxide 2-(a-methyl,2,6-dichlorobenzylthio) pyridine, l-oxide 2-(oc-II16tl1Yl,2,3,6-trichlorobenzylthio)pyridine, l-oxide 2- 2,4,5-trichlorobenzylthio pyridine, l-oxide2-(2,3,4-trichlorobenzy1thio)pyridine, l-oxide2-(2,4,6-trichlorobenzylthio)pyridine, l-oxide 2-( 2,4,5-tribron1obenzylthio pyridine, l-oxide 2-(2,4,6-tribromobenzylthio)pyridine, l-oxide 2-(2,3,6-tribromobenzylthio) pyridine, l-oxide2-(2,3,5,6-tetrachlorobenzylthio) pyridine, l-oxide and2-(2,3,4,S-tetrachlorobenzylthio)pyridine, l-oxide.

Benzyl thiopyridine oxides may be prepared by condensing the sodium saltof 2-thiopyridine, l-oxide with the corresponding benzyl halide. Theradical designated "ar,ar,ar-trichlorobenzyl was derived from mixedisomers of chlorinated toluene containing an average of three chlorineatoms in the carbocyclic ring. Ring chlorination of toluene producespredominately the 2,3,6-isomer and accordingly the major proportion ofthe product is 2,3,6- trichlorotoluene. The product may be prepared asdescribed by Kenneth L. Godfrey in United States Letters Patent2,977,210 issued March 28, 1961. Godfrey also describes chlorination inthe side chain to produce ar,ar,ar-trichlorobenzyl chloride. Brominationof the side chain produces an intermediate somewhat more reactive.Surprisingly, 2-(ar,ar,ar-trichlorobenzylthio)pyridine, l-oxide is amore effective herbicide than any com-. ponent known to be present. Bysubjecting them to the action of reducing agents the new compounds areconverted to the corresponding pyridines. The invention will be fullyunderstood and apparent from the detailed examples which follow.

Example 1 To a stirred solution of 30 grams (0.2 mole) of the sodiumsalt of 2-thiopyridine, l-oxide in 200 ml. of water was added in oneportion 25.4 grams (0.2 mole) of benzyl chloride and the mixture heatedat 50-60 C. for 5 hours. After cooling to 25 C., ml. of ethyl ether wereadded and the solution cooled to 10 C. with stirring. The precipitatewhich formed was filtered, washed with water until neutral to litmus andair-dried at 25-30 C. After recrystallization from ethyl alcohol,2-(benzylthio)pyridine, l-oxide was obtained in 50.9% yield as a tansolid melting at 170172 C. Analysis gave 6.17% nitrogen and 14.74%sulfur compared to 6.45% nitrogen and 14.76% sulfur calculated for C HNOS.

Example 2 In this example ar,ar,ar-trichlorobenzyl bromide was used inplace of benzyl chloride. 2-(-ar,ar,ar-trichlorobenzylthio)- pyridine,l-oxide in 72% yield was obtained as a tan solid melting at 229-230 C.after recrystallization from ethyl alcohol. Analysis gave 3.9% nitrogen,9.8% sulfur and 33.1% chlorine compared to 4.4% nitrogen, 10.0% sulfurand 33.2% chlorine calculated for C H Cl NOS.

Example 3 To 15 grams (0.1 mole) of the sodium salt of 2-thiopyridine,l-oxide in 100 ml. of water was added in one portion 23 grams (0.1 mole)of 2,3,6-trichlorobenzyl chloride and the mixture heated at 5060 C. for5 hours. After cooling to 10 C., 100 ml. of ethyl ether was added andthe solution stirred at 510 C. for one-half hour. The low melting solidswhich precipitated were removed and discarded. The filtrate was allowedto stand for two days. The precipitate which formed was filtered anddried at 25-30" C. 2-(2,3,6-Trichlorobenzylthio)pyridine, l-oxide wasobtained in 59.4% yield as a tan solid melting at 237-238 C. afterrecrystallization from ethyl alcohol. Analysis gave 4.40% nitrogen,9.88% sulfur and 33.18% chlorine compared to 4.4% nitrogen, 10.00%sulfur and 33.2% chlorine calculated for C H Cl NOS.

Example 4 Substituting 2,6-dichlorobenzyl chloride in the procedure ofExample 1, the solution was stirred for 15 minutes at 510 C. afteraddition of ethyl ether. The precipitate was collected by filtration,washed with water until neutral to litmus and air-dried at 2530 C.2-(2,6-Dichlorobenzylthio) pyridine, l-oxide was obtained in 66.4% yieldas a gray solid melting at 2l3216 C. Analysis gave 4.42% nitrogencompared to 4.89% calculated for C H Cl NOS.

Example 5 To a stirred solution of 15 grams (0.1 mole) of the sodiumsalt of Z-thiopy-ridine, l-oxide in ml. of water was added 18.5 grams(0.1 mole) of m-methylbenzyl bromide and the mixture heated at 50-60 C.for 5 hours. There was then added 200 ml. of water and the solutioncooled to 5 C. The precipitate which formed was filtered, washed withwater until neutral to litmus and air-dried at 25-30 C.Z-(m-methylbenzylthio) pyridine, l-oxide was obtained in 82.4% yield asa tan solid melting 3 at 108-110" C. after recrystallization from ethylalcohol. Analysis gave 5.92% nitrogen and 13.57% sulfur compared to6.06% nitrogen and 13.86% sulfur calculated The new compounds of thisinvention have general herbicidal properties. The method of controllingvegetation according to this invention comprises applying thereto atoxic concentration of the above defined benzyl thiopyridine oxides. Byapplying the toxicants to vegetation is meant any means whereby thetoxicant is brought into contact with living plants. The .toxicant maybe applied conveniently in the form of a spray containing the activeingredient in a concentration within the range of 0.l%10.0% by Weight.Thorough coverage of the foliage is effective for contact killing. Forpre-cmergence control amounts within the range of /260 pounds per acrehave been used successfully.

In general, in the application of these compounds aqueous dispersions oraqueous solutions depending on whether or not the compound is watersoluble, will be found most desirable. The dispersions will generallycontain a dispersing or wetting agent and the solutions also preferablycontain wetting agents to facilitate the spreading of the solution. Asdispersing and wetting agents there may be employed soft or hard sodiumor potassium soaps, alkylated aromatic sodium sulfon-ates such as sodiumdo-decylbenzene-sulfonate, or an amine salt of dodecylbenzenesulfonicacid, alkali metal salts of sulfated fatty alcohols, ethylene oxidecondensation products of alkyl phenols or tall oil and other dispersingand wetting agents. Petroleum hydrocarbon fractions, especially thosehigh in aromatic constituents, are desirable carriers. Particulate solidcarriers may be used where desired, as for example various clays, andthe toxicants applied in dust or granular form.

A spray containing various concentrations of the active ingredient shownin Table I was applied to the foliage of bean plants, to the foliage ofa mixture of grasses and finally to the foliage of a mixture ofbroadleaved plants. The mixture is indicated in the table as Broadleaf.A rating of indicates no phytotoxicity, 1 slight, 2 moderate and 3severe phytotoxicity.

The data recorded in Table II demonstrate pre-cmer- .gence activity. Thetoxicant was applied at the rate of 25 pounds per acre and thephytotoxicity observed.

TABLE II Active Ingredient Results Observed Severe phytotoxicity to crabgrass and pigweed; moderate phytotoxicity to sugar beet and foxtail.

Severe phytotoxicity to morning glory, wild oats, brome grass, ryegrass, foxtail, crab grass, pigweed and cotton; moderate phytotoxicityto mustard (radish), sugar beet, buckwheat and field bindweed.

Severe phytotoxicity to wild oats, foxtail, crab grass, pigweed and wildbuckwheat, moderate phytotoxicity to sugar beet and Sorghum.

2-(benzylthio)pyridine, 1-oxide 2(ar,ar,ar-trichlorobenzylthio)pyridine,l-oxidc.

2- (m-rnethylbenzylthio)pyridine,

l-oxide.

Furthermore, at 5 pounds per acre2-(ar,ar,ar-trichlorobenzylthio)-pyridine, l-oxide and2-(2,6-dichlorobenzylthio)py-ridine, l-oxide were severely toxic to wildoats, crab grass, pigweed, wild buckwheat, annual morning glory andsorghum.

It is intended to cover all changes and modifications of the examples ofthe invention herein chosen for purposes of disclosure which do notconstitute departures from the spirit and scope of the invention.

What is claimed is:

1. The method of controlling vegetation which comprises applying theretoa phytotoxic concentration of a benzylthiopyridine oxide having thegeneral formula where R is selected from the group consisting of monohalobenzyl, 2,3-, 2,4-, 2,6- and 3,6-dihalobenzyl, 2,3,4-, 2,3,6-,2,4,5- and 2,4,6-trih-alobenzyl, 2,3,4,5- and 2,3,5,6-

tetrahalobenzyl alpha-methyl 2,6-dihalobenzy1 and alphamethyl2,3,6-trihalobenzyl.

2. The method of controlling vegetation which comprises applying theretoa phytotoxic concentration of 2- (2,6-dichlorobenzylthio)pyridine,l-oxide.

3. The method of controlling vegetation which comprises applying theretoa phytotoxic concentration of 2- (polychlo'robenzylthio)pyridine,l-oxide in which the polych-lorobenzyl is composed of mixed isomerscontaining an average of three chlorine atoms in the benzyl radical.

4. The method of controlling vegetation which comprises applying theretoa phytotoxic concentration of 2- (2,3,6-trichlorobenzylthio)pyridine,l-oxide.

5. A herbicidal composition comprising a major proportion of aherbicidal adjuvant as carrier and a minor proportion sufficient toexert phytotoxicity of a phytotopic halobenzyl thiopyridine oxide havingthe general formula where R is selected from the group consisting ofmonohalobenzyl, 2,3-, 2,4-, 2,6- and 3,6-dihalobenzyl, 2,3,4-, 2,3,6-,2,4,5- and 2,4,6-trihalobenzyl 2,3,4,5- and 2,3,5,6- tetrahalobenzyl,alpha-methyl 2,6-dihalobenzyl and alpha- Inethyl 2,3,6-trihalobenzyl.

References Cited by the Examiner UNITED STATES PATENTS 2,826,584 3/1958Cislak. 2,922,792 1/1960 Rockett 712.5 X 2,932,647 4/ 1960 Rockett 712.5X 2,940,978 6/ 1960 Brown 712.5 X 3,107,994 10/ 1963 Rawlings et al712.5 X

FOREIGN PATENTS 758,658 10/ 1956 Great Britain.

OTHER REFERENCES Martin, Guide to Chemicals Used in Crop Protection, 3rdedition, 1957, page S40.

LEWIS GOTTS, Primary Examiner.

JAMES O. THOMAS, Examiner.

1. THE METHOD OF CONTROLLING VEGETATION WHICH COMPRISES APPLYING THERETOA PHYTOTOXIC CONCENTRATION OF A BENZYLTHIOPYRIDINE OXIDE HAVING THEGENERAL FORMULA